Electroforming low stress nickel



A ril 12, 1955 v. J. MARCHESE ELECTROFORMING LOW STRESS NICKEL Filed Nov. 15, 1951 0 :55 uwd 1:: A 2 1 m m m a 2 MM A w m; a W m 5 a L Q 2 |N5 4 $w\ Fw 3C a 2 2 F o 65432 0 IOOOO WA T715 BATH 6000 8000 o'zpos/r STRESS Les/0v INVENTOR VINCE/VT J. M/MCfi/ESE BY 6 7 K ATTORNEY United States Patent ELECTROFORMING LOW STRESS NICKEL Vincent J. Marchese, Valley Stream, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application November 15, 1951, Serial No. 256,536

3 Claims. (Cl. 204-3) This invention relates, generally to electroforming operations and the invention has reference, more particularly, to a novel method of producing electroformed nickel articles from a plating bath in such manner that the nickel is deposited in substantially stress free condition.

Nickel is a desirable material for plating purposes and for electroforming purposes, because of its superior physical properties. Thus, in the electroforming of ultra high frequency electrical equipment, such as Wave guides, concentric lines, directional couplers, etc., nickel ofiers advantages over such metals as copper and iron, because it has a greater rigidity than either iron or copper and because of its corrosion resistant properties. Thus, electroformed nickel microwave equipment can be made with a much thinner wall of metal (approximately 0.020 inch) and still be satisfactory from a mechanical consideration. Also, the resultant nickel wave guide would be almost as light in weight as the equivalent wave guide fabricated from aluminum. However, electrodeposited nickel as obtained from the various baths now in use, as for example, from a purified Watts type of nickel bath, usually has an internal tensile stress of approximately 12,000# p. s. i. or greater. This internal stress in the deposit is great enough to prevent removal of the electroformed nickel article from nondestructible mandrels such as steel, stainless steel, and Invar. When destructible mandrels such as zinc, low melting point alloys, and plastics are used, the electroformed nickel object or article will distort considerably upon removal of the mandrel, thus rendering the same useless for the purpose intended. This is caused by internal stresses that make it practically impossible to maintain close tolerances.

Heretofore, organic additions in nickel plating solutions have been used to reduce stress in the deposited metal. Thus, the organic agents, such as nickel formate, nickel acetate, and nickel citrate reduced the stress somewhat but to no great extent. Also, sodium naphthalene tri-sulfonate has been added to the Watts nickel bath and found the stress to be greatly reduced. Saccharin also has been used for the same purpose. However, tests show that the stability of saccharin and sodium napththalene tri-sulfonate as addition agents are uncontrollable and that uniform results cannot be obtained. Furthermore, the effects of adding these ingredients to the baths are short lived, so that a continuous monitoring of the bath must be maintained in order to use these materials.

Heretofore, some metal deposits have been made by superimposing alternating current on direct current during the plating cycle, the object being that the metal deposited during the cathodic pulse was partially redissolved during the anodic pulse. It was found that the deposition potential was periodically almost destroyed by the anodic pulse and that during the cathodic pulse the time was not sufficient for it to increase to any large value.

The principal object of the present invention is to provide a novel electroforming or electrodeposition method, whereby nickel is deposited with exceedingly low internal stress, such that the resultant product will not curl or crack and such that the same may be removed from mandrels without injury thereto.

Another object of the invention is to provide a novel method of electroforming of nickel articles by the superimposition of an alternating current on a direct current at an optimum voltage ratio of A.-C. to D.-C., whereby uniform results are obtained in the deposition of the metal. These and other objects will be readily apparent from the following specification and figures of which:

Fig. 1 is a diagrammatic view of the apparatus used in carrying out the present invention.

Fig. 2 is a graph showing the relationship of the ratio of A.-C. to D.-C. voltages used with respect to differing pH value of the plating bath;

Fig. 3 is a graph illustrating the variation in the stress of the deposited nickel resulting from changes in the A.-C./D.-C. voltage ratio; and

Fig. 4 is a graph showing the optimum ratio of A.-C. to D.-C. voltages used.

Referring now to Fig. 1 of the drawings, there is illustrated a tank 1 adapted to contain a nickel plating bath of the Watts type having a nickel anode 2 and a mandrel or cathode 3 upon which is to be formed a desired object of deposited nickel. A direct current source 4 is connected through leads 5 and 6 for supplying plating current to the bath through the electrodes 2 and 3. A direct current voltmeter 7 is shown connected across leads 5 and 6 for indicating the direct current voltage applied to the electrodes of the bath. A source of alternating sinusoidal current is connected to leads 8 which are connected in turn to a Variac 9 having a movable arm 10 for placing a desired voltage upon the primary of a transformer 11, which transformer is connected to leads 5 and 6 for superimposing an A.-C. voltage upon the D.-C. voltage applied across electrodes 2 and 3. A variable rheostat 12 is shown connected in lead 6 for adjustably controlling the voltages as applied to the electrodes. A D.-C. ammeter 13 is also connected to lead 6. A shunt circuit 14 is shown connected across the D.-C. voltmeter 7 and contains a rectifier 15 as of the crystal type and a condenser 16. Connected in shunt with thecondenser 16 is a vacuum tube voltmeter 17, which serves to indicate the inverse peak value of the A.-C. voltage supplied from transformer 11 to the electrodes 2 and 3 of the bath. The rectifier circuit 15, 16 enables the measuring also of the inverse peak of the superimposed A.-C. voltage across the nickel bath. As the first step of the improved method, a mandrel of the article to be formed is initially deposited in the Watts bath as the cathode thereof.

Many tests were run using Watts bath of progressively changing pH values. Also, a series of differing values of A.-C. voltage with a given value of direct current voltage were tried in connection with each bath so as to obtain the optimum values of pH for the solution and of A.-C./D.-C. voltage ratios to obtain the minimum stress in the deposited nickel. Also, the frequency of the alternating current was varied between approximately 60 cycles and 400 cycles to determine the most suitable superimposed alternating current frequency. The graph in Fig. 2 shows a curve giving the minimum values of stress in the deposited nickel for baths of different pH values and different values of A.-C./D.-C. voltage ratios. It will be noted that the minimum stress is obtained with a Watts solution having a pH value of 4.5 at which time the A.-C./D.-C. voltage ratio is substantially 3, the optimum ratio. Any substantial departure from these values will result in greatly increased residual stress of the deposited nickel causing deformation of the electroformed article upon removal from its mandrel. However, when the stress is reduced to the neighborhood of 2000# per square inch, due to the use of a bath of approximately 4.5 pH and a ratio of A.-C. voltage/D.-C. voltage of substantially 3 using 60 cycle superimposed alternating current, no deformation occurs after removal from the mandrel. As a typical example, a D.-C. voltage of 1.35 volts was used as against a superimposed A.-C. voltage of 4.05 volts.

Fig. 3 is a graph showing the A.-C./D.-C. voltage ratio plotted as ordinates and deposit stress in pounds per square inch as abscissae. Two curves are illustrated, one using 60 cycle current and the other using 400 cycle current. It will be noted that the point of minimum stress obtains in using the 60 cycle superimposed voltage and a voltage ratio of substantially 3. It will be noted that the minimum stress obtaining when a 400 cycle current is used is higher, i. e., in the neighborhood of 5000# per square inch. In making the test shown in Fig. 3,

the pH value of the Watts bath was 4.5, the current density was 50 mnperes per square foot, the temperature of the bath being 145 Fahrenheit and there being no H202 present, although Duponal M. E. dry wetting agent was used to eliminate pitting.

In Figure 4, there is shown graphically the ratio of the A.-C. superimposed voltage to that of the D.-C. voltage, it being rotated that the peak AC. voltage has substantially three times the magnitude of the D.-C. voltage under conditions of residual stress indicated at point A of the graph in Figure 3. In carrying out the test, it was found in superimposing 60 cycle A.-C. voltage upon the D.-C. voltage, that the stress in residual nickel was greatly reduced by the order of at least one-half. In order for the stress to be reduced appreciably, the peak AC. voltage must be greater than the D.-C. voltage. A pH of 4.5 gives a lower stress value than a pH of 2.0 and at a pH of 5 or above, the stress value increases sharply, as indicated in Figure 2. 60 cycle alternating current produced argreater reduction of stress in the deposit at both pH of 2.0 and 4.5 than 400 cycle alternating current. In the electrodeposition operation, the density of the D.-C. through the bath may be Varied between and 50 amperes per square 'foot. Before the method step of removing the electroformed article from the mandrel, the electroformed nickel article and mandrel are withdrawn from the bath.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departure from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A method of producing electroformed nickel articles which comprises immersing as a cathode a mandrel of the article to be formed and a nickel anode in a Watts plating bath with a pH value of substantially 4.5, subjecting the bath to a direct plating current of between 10 and 50 amperes per square foot and D.-C. voltage having a superimposed A.-C. voltage of a peak magnitude of substantially three times that of the D.-C. plating voltage to electrodeposit nickel having minimized internal stress upon the mandrel, Withdrawing the electroformed nickel article and mandrel from the bath, and removing the electroformed nickel article from the mandrel.

2. A method of producing electroformed nickel articles which comprises immersing as a cathode a mandrel of the article to be formed and a nickel anode in a Watts plating bath with a pH value of substantially 4.5, subjecting the bath to a direct plating current of between 10 and amperes per square foot and D.-C. voltage having a superimposed A.-C. cycle voltage of a peak magnitude of substantially three times that of the D.-C. plating voltage to electrodeposit nickel having a mini mized internal stress of less than approximately 2000 pounds per square inch upon the mandrel, withdrawing the electroformed nickel article and mandrel from the bath, and removing the electroformed nickel article from the mandrel.

3. A method of producing electroformed nickel articles which comprises immersing as a cathode a mandrel of the article to be formed and a nickel anode in a Watts plating bath at a temperature of approximately Fahrenheit with a pH value of substantially 4.5, subjecting the bath to a direct plating current of between 10 and 50 amperes per square foot and D.-C. voltage having a superimposed A.-C. voltage of .a peak magnitude of substantially three times that of the D.C. plating voltage to electrodeposit nickel having a minimized internal stress upon the mandrel, withdrawing the electroformed nickel article and mandrel from the bath, and removing the electroformed nickel article from the mandrel.

References Cited in the file of this patent UNITED STATES PATENTS Chester July 18, 1950 Zapponi Nov. 25, 1952 OTHER REFERENCES 

1. A METHOD OF PRODUCING ELECTROFORMED NICKEL ARTICLES WHICH COMPRISES IMMERSING AS A CATHODE A MANDREL OF THE ARTICLE TO BE FORMED AND A NICKEL ANODE IN A WATTS PLATING BATH WITH A PH VALUE OF SUBSTANTIALLY 4.5, SUBJECTING THE BATH TO A DIRECT PLATING CURRENT OF BETWEEN 10 AND 50 AMPERES PER SQUARE FOOT AND D.-C. VOLTAGE HAVING A SUPERIMPOSED A.-C. VOLTAGE OF A PEAK MAGNITUDE OF SUBSTANTIALLY THREE TIMES THAT OF THE D.-C. PLATING VOLTAGE TO ELECTRODEPOSIT NICKEL HAVING MINIMIZED INTERNAL STRESS UPON THE MANDREL, WITHDRAWING THE ELECTROFORMED NICKEL ARTICLE AND MANDREL FROM THE BATH, AND REMOVING THE ELECTROFORMED NICKEL ARTICLE FROM THE MANDREL. 